GREEN THUMBS UP: Winter protection for trees, shrubs, and gardens

By Suzanne Mahler

Saturday

Jan 6, 2018 at 2:00 PM

The past week featured a rollercoaster ride of temperature fluctuations and weather conditions. Although I welcomed the intermittent spurts of milder temperatures which permitted me to rescue numerous potted orphans from the frozen ground for transfer into my garage and protected areas along my home’s foundation, these variations in temperature pose serious challenges for many of our treasured plants.

For the next three to four months, the majority of our plants will remain dormant as fluctuating temperatures, chilly winds, snow, and ice challenge their very existence. Most gardeners have a major investment in the trees and shrubs growing along their foundations and in their landscapes. Even if these plants were purchased as small specimens, as they mature over the years, their value increases exponentially.

Broad-leafed evergreen plants, especially boxwood, rhododendrons, azaleas, Leucothoe, and hollies, face the greatest hazards. Subjected to recent droughts, desiccating winds, and winter sun, their leaves may be scorched, particularly during the latter half of the winter. Apply anti-desiccant sprays when temperatures are above freezing to protect their leaf surfaces.

Evergreen trees and shrubs, especially arborvitaes and woody specimens planted along foundations where snow slides off the roof, should be protected from the possible weight of future snowfalls. Using a roll of soft cord or heavy twine, attach the twine to the base of the tree’s trunk and wind around the branches in an upward spiral to the top and back down again. During the winter, monitor these plants and carefully brush away accumulating snow. Melting water may drip onto these shrubs, turning to ice as temperatures drop. If strong winds follow, further damage may occur.

Poor winter drainage and alternate freezing and thawing of damp soils tend to be the major causes of perennial plant losses during the winter months. Shallow-rooted plants and late season transplants are the most susceptible, heaving out of the ground during freeze-thaw cycles, exposing roots to cold, dry winds or severing the roots from the crowns of the plants. The application of winter mulches, once the ground has frozen, is an ideal means of protecting dormant plants from variable temperatures.

Mulches applied too early in the season may encourage destructive pests to take up residence and feed on plants but by this time of year, most of these critters have found refuge elsewhere assuming that leafy debris was removed. The purpose of winter mulches is to keep the ground frozen, not to keep the plants beneath the mulch warm and cozy. During typical winters, daytime temperatures often rise above freezing, thawing the upper inch or two of the soil surface. As temperatures plummet after nightfall, this upper layer freezes again. A 2 to 3-inch layer of winter mulch spread over root systems should prevent heaving as this covering will undergo the freeze-thaw cycle, enabling the earth beneath to remain frozen. A periodic inspection of the perennial borders during warming trends throughout the winter months is advisable. Plants that have heaved out of the ground can usually be gently pushed back into the soil on warm days.

While several inches of snow are the ideal winter protection for our gardens, most winters feature weeks with little or no snow cover. A layer of compost, pine bark mulch, or shredded leaves applied over root systems offers the added benefit of providing moisture-retentive, organic matter that will continue to break down during the winter months and can be worked into the soil in early spring. Care should be taken not to bury the crowns of evergreen perennials with basal foliage, as this can lead to rot or suffocation. White pine needles are a light, airy alternative, staying in place as they have a tendency to cling to one another, while providing a protective cover that can be easily removed once temperatures moderate in the spring.

Evergreen boughs from our Christmas tree will be used in the coming weeks to cover many of my evergreen perennials, including candytuft, ground phlox, coral bells, and pinks that may be subject to winterburn as a result of dry, desiccating winter winds and intense winter sunlight while deterring foraging deer and bunnies. I also stockpile bags of bark mulch and soil in my garage to distribute around fall transplants that heave during freeze/thaw cycles.

Take time on mild winter days to inspect and protect your investment in plant material and enjoy the sights and sounds of winter.

Suzanne Mahler is an avid gardener, photographer and lecturer. She is a member of a local garden club, past president of the New England Daylily Society, an overseer for the Massachusetts Horticultural Society and is employed at a garden center.

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